Materials that have retroreflective microcubes formed thereon or glass beads deposited thereon possess a property that incident light is reflected back in a direction from which it originates. This makes the materials popular for use in a wide range of products that require a retroreflective attribute. The materials are particularly useful for safety applications reasons, including signage, construction barriers, traffic barriers, personal protection gear and the like.
There are two different ways to make materials retroreflective. One method uses microscopic beads to form what is generally referred to as “beaded sheets.” The microscopic beads may have a metallized coating to improve performance and the microscopic beads may be deposited on a surface of sheeting, or film, or be partially or fully embedded in the sheeting. The second method uses microprisms, commonly referred to as prismatic sheeting. Prismatic sheeting uses cube-cornered, triangles, hexagons, squares and rectangles to bounce back reflected light.
Generally, the prismatic sheeting is brighter than beaded sheeting. In terms of interchangeability of beaded sheeting and prismatic sheeting, it would be very difficult to make the prismatic sheeting perform just like the beaded sheeting. Likewise, it would be impossible to make the beaded sheeting perform just like the prismatic sheeting.
A highway sign made with beaded sheeting could be replaced by a second sign with prismatic sheeting, but there would be a difference since the prismatic sheeting would be a little brighter during both day and night. Sometimes highway signs are made with beaded sheeting for a sign background, while the prismatic sheeting is used for cutout letters. However, beaded sheeting and prismatic sheeting are not combined as materials for the sign background, and it is rare to use a mixture of beaded sheeting letters and prismatic sheeting letters. At certain angles, differences in the beaded sheeting and prismatic sheeting would be quite noticeable and could cause confusion.
In a retroreflective field, a standard applied to retroreflective sheeting is decided by specifications set by road management authorities, such as the Federal Highway Administration (FHWA), Department of Transportation (DOT), etc. In addition, standards set forth by the American Society for Testing and Materials (ASTM) are also taken into consideration. ASTM is an international standards organization that develops technical standards for a wide range of products and materials. The specifications are mainly based on retroreflective performance, which is an amount of retroreflected light that is returned from retroreflective sheeting.
Retroreflective sheeting is manufactured to pass these specifications, and typically, manufactured retroreflective sheeting has values much higher than the specifications or standards. The sheeting is then processed to make roadside traffic signs for highways, city roads or used in other safety applications such as vests, cones or barriers.
The performance of the retroreflective sheeting degrades due to natural elements such as sunlight, ultraviolet light, heat and dust. In addition, retroreflective sheeting degrades from poor maintenance during use. Over its lifetime, retroreflectivity of the retroreflective sheeting may be reduced. As performance diminishes, it is important for road authorities and safety inspectors to inspect signs and safety devices as well as compare the retroreflective sheeting with relevant specifications or standards to ensure that the retroreflective sheeting is still functional and safe.
A most accurate way for an inspection is through the use of a hand-held retro reflectometer, which reads the sign and displays the value of specific intensity per unit (SIA). This method is both time consuming and expensive.
Hence this inspection is almost always done visually by comparing the sign or safety device with the relevant specification or standard. The main challenge is to make available a standard which will accurately match the specifications.
What is needed therefore is a method by which to better control and improve the performance of both beaded and prismatic sheeting without the need to mix different types of reflective materials and to provide retroreflective sheeting that can be changed or manipulated in order to routinely meet the relevant specification or standard that has been selected.